1. Field of the Invention
The present invention relates to an alkali-manganese battery containing manganese dioxide as positive electrode active material, and more particularly to an improvement of the positive electrode active material.
2. Description of the Related Art
In conventional alkali-manganese batteries, there have been used positive electrode active materials comprising a mixture of manganese dioxide particles and powdery carbon which was added to enhance the electroconductivity between the manganese dioxide particles as well as to improve the electroconductivity between a positive electrode can and the positive electrode active material contained therein instead of the use of manganese dioxide (ordinarily electrolytic manganese dioxide) particles alone as positive electrode active material because manganese dioxide itself has quite a low specific conductivity.
A higher content of powdery carbon in the mixed positive electrode active material gives rise to a reduced proportion of the manganese dioxide active material to be charged in the specific volume in the battery, which receives the mixture of the manganese dioxide active material and the powdery carbon. This causes a reduction in the discharge capacity of the battery, though the internal resistance of the battery is reduced. On the other hand, a lower content of powdery carbon increases the proportion of manganese dioxide to be charged in the battery with an increase in the internal resistance thereof. Since the increase in the proportion of the manganese dioxide active material to be charged opposes the reduction in battery's internal resistance of the battery in a manner as described above, it is important to achieve a compromise between them.
In order to achieve a compromise between the both requirements of increasing the amount of the manganese dioxide active material to be charged and of reducing the battery's internal resistance, there has been proposed the use of a positive electrode active material comprising a mixture of manganese dioxide particles and a 10% or more of carbon particles having the same average particle size as that of the manganese dioxide particles as disclosed in JP54-26426A and JP63-232266A).